The objective of this project is to increase our understanding of the genetic basis of cellular differentiation. The in vitro differentiation of Drosophila neurons and myocytes, from their respective blast cells, is the experimental system on which genetic and developmental analysis is being performed. In addition to alleles of two known mutants (supplied by T. Wright and J.D. Mohler), we have induced 36 recessive embryonic lethals or maternal lethals which affect neuron and/or myocyte differentiation in vitro. EMS and ICR-170 are being employed as mutagens. The 40 mutations are distributed among the three major chromosomes; 12 on the X, 13 on the second and 14 on the third chromosome. Complementation analysis has resolved 27 complementation groups. Through the analysis of mutants which affect neuron and/or myocyte differentiation, we propose to piece together the gene directed steps (unique and common) in the differentiative pathway. Phase contrast observation of single embryo cultures has allowed determination of earliest culture signs of abnormal differentiation caused by a specific mutation. This determination has been accomplished for three complementation groups to date. BIBLIOGRAPHIC REFERENCES: Donady, J. James and Eric Fyrberg 1976. Mutants of Muscle Cell Differentiation in Drosophila (abstract). Genetics (in press). Fyrberg, Eric and J. James Donady 1976. An Improved Screen for Autosomal Recessive Lethals. Dros. Info. Serv. (in press).